The level of relative movement between a semi-annular thrust washer (also known as a thrust flange) and the semi-cylindrical journal bearing shell to which it is connected is of great importance, with respect to providing greater uniformity of wear within a bearing assembly, and ensuring correct assembly.
It is known to machine the bearing shells and washers of half-bearings in a single piece construction. Commonly, it is also known to firmly connect thrust washers to a bearing shell. For example, it is known to firmly and permanently connect thrust washers to a bearing shell by inserting lugs that are located on the inner periphery of the thrust washer into open-ended recesses in the axial end faces of the bearing shell, before mechanically deforming the bearing shell adjacent to the recesses to trap the lug within a dovetail connection. Such a flanged half-bearing is disclosed in GB2225392. It is also known to form such firm connections by use of tightly fitting dovetail shaped connections.
In use, flanged half-bearings are located within a housing, such as an engine block. Disadvantageously, a rigid connection between the thrust washers and the bearing shell can lead to unwanted gaps between the thrust washers and the housing. Such gaps can result in regions of unsupported load that could result in flexure and fatigue of the washers.
Furthermore, a rigid connection between the thrust washers and the bearing shell can result in a reduced contact area between the thrust washers and the housing, which provides poor heat transfer between the thrust washers and the housing, and may result in overheating of the thrust washers, leading to a reduction in the viscosity of the lubricating oil. A reduced oil viscosity leads to a reduction in the oil film thickness, resulting in increased wear of the bearing shell and the thrust washer.
Further, in the case that the connection is made by mechanical deformation of the bearing shell, this causes swelling of the surrounding material. In such cases it is typically necessary to perform a post-connection machining stage to remove the material swell that projects from the cylindrical inner surface of the bearing shell, which increases costs and prevents the use of performance enhancing coatings on the inner surface of the bearing shell.
It is also known to connect thrust washers to a bearing shell with hooking lugs projecting from and close to the ends of the internal periphery of the thrust washer, which loosely connect within open-ended hooking recesses in the axial end faces of the bearing shell. The bearing is assembled by elastically reducing the radius of curvature of the bearing shell before aligning with the thrust washers, such that the bearing shell radially expands back into shape, when released, and is loosely retained on the thrust washer. Such a bearing is disclosed in U.S. Pat. No. 4,533,261.
Disadvantageously, such a thrust washer is not connected to the bearing shell circumferentially intermediate the two hooking lugs and, in use, can experience a level of relative axial movement in that region that causes enhanced wear. Further, the design of hooking lug that is particularly favourable for the purposes of assembly provides only a limited amount of resistance against rotation of the thrust washer about the axis of the crankshaft, within the housing, which is particularly damaging. Additionally, such thrust washers can be vulnerable to incorrect assembly, potentially including damage occurring during the incorrect assembly, both of which can further enhance wear during use.